LEDs can be used both for illumination and as indicators. They can also be arranged as 7-segment displays or as tiny pixels in an OLED (organic LED) display.
This chapter contains recipes relating to powering and controlling LEDs as well as for using a display with an Arduino or Raspberry Pi.
14.1 Connect Standard LEDs
Problem
You want to connect a standard low-power LED to a GPIO pin, but you are not sure what value of series resistor to use.
Solution
Back in Recipe 4.4 you saw how an LED needs a series resistor to prevent too much current from flowing. Too much current will shorten the life of an LED, but more importantly, it may damage or destroy the Arduino or Raspberry Pi GPIO pin that is controlling the LED.
Wire up your LED to a GPIO pin as shown in Figure 14-1 and then use Table 14-1 to select a value for the series resistor.
Figure 14-1. Connecting an LED to a GPIO Pin
Table 14-1. LED Series Resistor Values
Infrared
Red
Orange/Yellow/Green
Blue/White
Violet
UV
Vf
1.2-1.6V
1.6-2V
2-2.2V
2.5-3.7V
2.7-4V
3.1-4.4V
3.3V GPIO 3mA
1kΩ
680Ω
470Ω
270Ω
220Ω
68Ω
3.3V GPIO 16mA
150Ω
120Ω
82Ω
56Ω
39Ω
15Ω
5V GPIO 20mA
220Ω
180Ω
150Ω
150Ω
120Ω
100Ω
Discussion
In practice, nearly all LEDs will illuminate to some degree even from 3.3V with a 1kΩ resistor limiting the current. So, as an even broader rule of thumb, ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month, and much more.
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.
Julian F.
Head of Cybersecurity
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.
Addison B.
Field Engineer
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.
Amir M.
Data Platform Tech Lead
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.
